Can freestyle render edges with no face?
Unfortunately this isn't supported (yet):


  Known Limitations and issues
  
  
  FreeStyle is only available for the Blender Internal renderer.
  Highly memory demanding: All mesh objects in a render layer are loaded at once.
  Only faced mesh objects are supported. The following kinds of meshes are ignored.
  
  
  Mesh faces with wire materials.
  Mesh faces with completely transparent materials. 
  
  Transparent faces are treated as opaque faces.
  No edges at face intersections are detected yet.
  Layer masks do not work with Freestyle.
  Freestyle rendering results do not have any Z depth information.
  Does not work with a panoramic camera.
  


Emphasis mine. Note that Freestyle is available in the latest development builds and will be in 2.72.

Perhaps it will be supported someday, but for now you'll have to try something else. See How can I render an edge only mesh as solid lines? for alternatives.